RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
The SCSS test accelerator was constructed and user experiments using SASE-FEL light in an extreme-ultraviolet (EUV) region have been performed at SPring-8. It is necessary to distribute an accurate timing signal both to accelerator components and experimental instruments. We developed a trigger system targeted as a timing jitter of less than 100 fs. The jitter of the time difference between the reference timing signal and a beam-induced signal from an RF BPM cavity was measured. The jitter value was nearly 50 fs in rms. However, this value was measured with electron beams after C-band accelerator cavities and not measured with the SASE light pulses at the experimental end station. Therefore, we employed an in-vacuum fast photo diode in order to directly observe EUV light at a 60 nm and to detect the arrival timing at the end station. The measured time jitter was 2.5 ps in rms, which was limited by the photo diode. Even thorough the resolution of the time jitter did not reach to 50 fs, the system is still usable to verify trigger delay values for user experiments. This fast timing measurement using the in-vacuum photo diode is still a pioneer of optical technology in an FEL field.
SOLEIL, Gif-sur-Yvette
Imagine Optic, Orsay
BNL, Upton, Long Island, New York
LOA, Palaiseau
RIKEN/SPring-8, Hyogo
JASRI/SPring-8, Hyogo-ken
The VUV Self-Amplified Spontaneous Emission of the SPring-8 Compact SASE Source (SCSS) Test Accelerator is characterized at different stages of amplification up to saturation [1]. Experimental measurements are performed by use of a VUV Hartmann wavefront sensor. This kind of sensor gives access to both intensity and phase profiles of the incoming beam. We characterize the mode selection when approaching the saturation regime of the FEL. Optical quality of the saturated SASE radiation is measured to be better than Lambda/5 PV and Lambda/22 rms (Lambda = 61.5 nm) depending on the machine optimization. Moreover, pointing of the beam as well as spatial structure, size and position of the source are retrieved and their shot-to-shot fluctuations investigated. Analytical [2] and numerical calculations [3], using SRW and GENESIS codes, show good agreement with the experimental measurements. All these elements are of crucial importance for a better understanding and optimization of the FEL and of course for user applications requiring a stable focused beam on their samples. We are grateful to the SCSS Test Accelerator Operation Group at RIKEN for continuous support in the course of the studies
[1] R. Bachelard et al., "Wavefront and Transverse Structure of the FEL Self-Amplified Spontaneous Emission", to be submitted
[2] M. Xie, NIMA 445, 59(2000)
[3] O. Chubar et al., Proc. EPAC-98, 1177(1998)
